The present invention involves an improved subsea wellhead structure in which the casing hanger, the seal around the casing hanger and the bore protector are run into the wellhead housing on a single running string.
In prior subsea wellhead structures, casing hangers have been run on a string and have included a split ring to latch the hanger in position when it is landed, a passage around the hanger through which fluid may flow during cementing and a seal which is movable into position to seal the passage after the completion of the cementing. The seal includes a resilient member between rings and is set by rotation of the setting sleeve with a setting tool. This structure is illustrated in U.S. Pat. No. 3,273,646.
U.S. Pat. No. 3,350,130 discloses a similar structure in which there is also a seat protector included in the structure run into the well bore with the casing hanger which is releasably connected to the actuating sleeve for setting the hanger seal.
Another similar structure is shown in U.S. Pat. No. 3,489,436 in which the mandrel is releasably connected by locking segments which are released by a pressure responsive device which is activated by a plug seated within the mandrel.
The hanger seal shown in U.S. Pat. No. 3,797,864 includes a resilient seal backed up at each end by metal end caps with inner and outer legs which engage the surfaces in metal-to-metal sealing engagement and present extrusion of the resilient seal ring.
These prior art structures all rely upon a resilient sealing ring for the sealing between the exterior of the hanger and the interior of the wellhead housing. They also have complicated structures for release of the running tool and for recovery of the protection sleeve. Another disadvantage of the devices of the prior art is that they require a washing step following the cementing step to clean the sealing surfaces.